Recently, downsizing of radio communication terminals, which may be typically cellular phones, has progressed. For downsizing, it is studied to reduce the number of parts used in the radio communication terminals. The number of parts used in the radio communication terminals may be achieved by omitting an interstage filter provided in a transmission path or a reception path. However, it is required to improve the isolation characteristic between a transmission terminal of a duplexer and a reception terminal thereof.
Japanese Patent Application Publication Nos. 2006-60747 and 2002-76879 describe improvements in the isolation characteristic of the duplexer by removal of unwanted electromagnetic couplings.